It wasn't mentioned in the article, but the temperature of the water was 10°C. A 15-minute plunge at that temperature seems a bit long to me. I did daily cold plunges for about 6 months, ranging from 6° to 15°C, and 5 to 15 minutes. The sweet spot for me was that the water had to be colder than 10°C, but the length of the plunge didn't need to be for more than 5 minutes. I'd be curious to know if it improved my blood pressure - perhaps I need to get a blood pressure monitor to track this.